import com.fasterxml.jackson.databind.ObjectMapper;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

class Message {
    public String from;
    public String to;
    public String message;
}
@WebServlet("/message")
public class MessageServlet extends HttpServlet {
    private ObjectMapper objectMapper=new ObjectMapper();
   // private List<Message> messages=new ArrayList<>();

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //处理提交消息的请求
        Message message=objectMapper.readValue(req.getInputStream(),Message.class);
        // 最简单的保存方法就是保存到内存中.
        // messages.add(message);
        // 通过 ContentType 来告知页面, 返回的数据是 json 格式.
        // 有了这样的声明, 此时 jquery ajax 就会自动的帮我们把字符串转成 js 对象.
        // 如果没有, jquery ajax 就只是当成字符串来处理的~~
        save(message);

        resp.setContentType("application/json; charset=utf8");
        resp.getWriter().write("{\"ok\":true}");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取到消息列表
        // 获取到消息列表. 只要把消息列表中的内容整个的都返回给客户端即可
        // 此处需要使用 ObjectMapper 把 Java 对象, 转成 JSON 格式字符串~
        List<Message> messages=load();
        String jsonString=objectMapper.writeValueAsString(messages);
        System.out.println("jsonString"+jsonString);
        resp.setContentType("application/json; charset=utf8");
        resp.getWriter().write(jsonString);

    }

    private void save(Message message){
        //把一条消息保存到数据库中
        Connection connection=null;
        PreparedStatement statement=null;
        try {
            //1.和数据库建立连接
            connection=DBUtil.getConnection();
            //2.构造SQL
            String sql="insert into message values(?,?,?)";
            statement=connection.prepareStatement(sql);
            statement.setString(1,message.from);
            statement.setString(2,message.to);
            statement.setString(3,message.message);
            //3.执行SQL
            statement.executeUpdate();
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,null);
        }

    }
    private List<Message> load(){
        //获取数据库中所有的信息
        List<Message> messages=new ArrayList<>();
        Connection connection=null;
        PreparedStatement statement=null;
        ResultSet resultSet=null;

        try {
            connection=DBUtil.getConnection();
            String sql="select * from message";
            statement=connection.prepareStatement(sql);
            resultSet=statement.executeQuery();
            while (resultSet.next()){
                Message message=new Message();
                message.from=resultSet.getString("from");
                message.to=resultSet.getString("to");
                message.message=resultSet.getString("message");
                messages.add(message);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }finally {
            DBUtil.close(connection,statement,resultSet);
        }
        return messages;
    }
}
